Cells from the two ends move toward each other, touch, and join. The fish swims away.

This image shows the motoneurons (in green) move to fill the gap in the baby zebrafish's spinal cord. The whole process occurs in less than two days.Credit:Dr Jan Kaslin

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Here's a close-up.Credit:Dr Jan Kaslin

The entire process, from paraplegia to movement, can take less than two days.

“They are remarkably unharmed by having their spinal cords severed,” says Dr Jan Kaslin. “After a day or two they go swimming away”.

It has now been caught on film for the first time (helpfully, young zebrafish are transparent), presented to the International Society for Stem Cell Research annual meeting in Melbourne on Thursday.

Dr Jan Kaslin, pictured here at FishCore with some of the fish he studies.Credit:Joe Armao

Stem cells live throughout the bodies of zebrafish, where their ability to make almost any type of new cell helps the creatures recover from grievous injuries.

Our bodies have these stem cells too, but – for reasons scientists are still trying to understand – they are often dormant.

Dr Kaslin, who took the footage and pieced-together the process using the Australian Regenerative Medicine Institute's FishCore – an aquarium based at Monash University with 6200 zebrafish-filled tanks, set up as a sort of living database - thinks zebrafish might offer key insights into how we can reactivate these cells.

His fascination with the creatures started when he was hunting a cure for Parkinson’s, a disease that kills neurons in the brain.

To test treatments, first you need to induce Parkinson’s in an animal. Zebrafish, which share at least 70 per cent of their important genes with humans, were a logical option.

But every time Dr Kaslin’s team removed neurons in the fish’s brain, they quickly grew back.

“That led me to thinking these fish might be able to regenerate neurons,” he says.

Now thatDr Kaslin has been able to prove the fish can regrow not just their brains but also their spinal cords, he hopes the knowledge can be applied to humans.

Researchers around the world are hunting for ways to coax the body's dormant stem cells into growing new cells. The zebrafish footage suggests they may have been looking in the wrong place.

Rather than using stem cells to grow a new spinal cord, the zebrafish directs existing cells to first bridge the gap. Then, stem cells come in over the top to finish repairs.

A ‘bridge’ or scaffold of existing cells might be important to prompt dormant stem cells into action.

Various trials around the world are already attempting this right now, inserting ‘bridge’ cells into damaged spines before introducing stem cells. The results will be closely watched around the world.

“Producing something new from a stem cell takes a lot of time. By being able to use existing tissue to kickstart the process, it’s much quicker,” says Dr Kaslin.

“It allows the animal to regenerate much faster – which is very important. If your spine or brain does not work, you will be relatively quickly dead.”